1. Field of the Invention
The present invention relates to a knocking presence evaluation circuit in an internal combustion engine.
More specifically the invention relates to a knocking presence evaluation circuit in an internal combustion engine having at least a pressure sensor facing a combustion chamber for each cylinder comprised in the engine itself and suitable to detect a pressure signal.
The invention also relates to a knocking identification and control system associated with an internal combustion engine.
The invention finally relates to a processing method of a pressure signal for the detection and evaluation of a combustion phenomenon in an internal combustion engine.
2. Description of the Related Art
As it is well known, knocking phenomena are particularly dangerous for internal combustion engines with controlled spark, implying, besides the emission of a characteristic metallic noise (the so called combustion shock), a whole series of consequences which can seriously damage the engine itself.
Knocking phenomena are in fact particularly dangerous for such engines, implying a whole series of consequences which can seriously jeopardize the operation thereof.
In fact, vibrations, engine power losses, increased heating are generally associated with knockings, reaching, under particularly severe conditions, the breakage of the engine mechanical parts.
In particular, the increased thermal charges, together with the mechanical stresses, can lead to the breakage of some components of the engine (such as pistons, piston rings, head gasket, valves, etc.) due to a well known hot fatigue phenomenon.
The identification and the analysis of the knocking phenomena in controlled spark engines thus represents an important factor for the electronic control of these engines.
For implementing a knocking control and identification strategy it is also known to use sensors suitable to monitor the combustion process which occurs inside an internal combustion engine, in order to evaluate the knocking presence and thus provide a control unit of the engine itself with a feedback.
Most engines currently on the market use suitable acoustic or accelerometric sensors (set on the frequency band 3-20 kHz) to detect the knocking presence.
Such sensors are placed in the engine block and they allow to identify the knocking presence in the combustion chamber through the detection of the vibrations induced in the engine block.
Although advantageous under several aspects, this first solution has various drawbacks.
First of all, the sensors carry out an indirect measure of the knocking presence. In such case, the signal received through these sensors can be contaminated by disturbs independent from the knocking presence, such as for example, the natural mechanical vibrations the engine structure is subjected to during the operation thereof at high revolutions, vibrations which however do not depend on the knocking presence.
Moreover, in the case of some types of vibrational sensors such as resonant sensors, it is necessary to provide different sensors according to the type of engine.
To overcome these drawbacks a knocking presence identification method is alternatively known which analyzes a signal received from a pressure sensor facing directly in the engine combustion chamber.
When the engine is subject to knocking, in fact, the pressure cycles in the combustion chamber have typical oscillations with width peaks gradually decreasing in time whose frequency (oscillating between 3 and 20 kHz) depends on the propagation speed of the pressure waves in the cylinder during the knocking phenomenon, as schematically shown in FIG. 1.
A known model to identify the knocking presence starting form the pressure cycle in combustion chamber acquired by a pressure transducer facing directly in such chamber is described for example in the article by F. Millo and C. V. Ferraro entitled: “Knock in S.I. Engines: A Comparison Between Different Techniques for Detection and Control”, SAE paper 982477, 1998.
In practice, however, this model and the others currently in use, provide a quite laborious, and in some cases little efficient, analysis of the pressure signal so as to discriminate the detonation presence or absence. In particular, it is known to use a predetermined knocking intensity critical threshold, beyond which the intervention of the engine unit control is started.